In order to obtain adequate exposure, a partial-thickness suture can be passed through the superior cornea to rotate the eye inferiorly (Fig 13-4A). Alternatively, a superior rectus bridle suture can be placed (Fig 13-4B); however, its use has been reported to increase the risk of trabeculectomy failure.
The conjunctival incision can be made in 1 of 2 locations. A fornix-based trabeculectomy conjunctival flap is created by making an incision adjacent to or slightly posterior to the limbus (Fig 5-13; Video 13-2), while a limbus-based trabeculectomy flap is created by making an incision 8–10 mm posterior to the limbus (Fig 6-13). Fornix-based trabeculectomies offer the advantages of better exposure, while limbus-based flaps reduce the risk of early wound leak because the incision is several millimeters away from the scleral flap. Fornix-based flaps are associated with more diffuse blebs.
Figure 13-4 Options for trabeculectomy exposure. A, Corneal traction suture. B, Superior rectus bridle suture.
(Part A courtesy of Keith Barton, MD; part B courtesy of Alan Lacey. Both parts reproduced with permission of Moorfields Eye Hospital.)
Figure 13-5 Fornix-based conjunctival flap. A, Drawing shows the initial incision through conjunctiva at the limbus and the insertion of the Tenon capsule. The arc length of the initial incision is approximately 6–7 mm. Tissue adjacent to the incision is undermined with blunt scissors before the scleral flap is prepared. B, Incision is closed either at both ends with interrupted or purse-string sutures or with a running mattress suture.
(Modified with permission from Weinreb RN, Mills RP, eds. Glaucoma Surgery: Principles and Techniques. 2nd ed. Ophthalmology Monograph 4. American Academy of Ophthalmology; 1998:43.)
Figure 13-6 Limbus-based conjunctival flap. A, Drawing shows the initial incision through conjunctiva and Tenon capsule. B, Clinical photograph corresponding to part A shows the initial incision for creation of a limbus-based conjunctival flap. C, Completion of conjunctiva–Tenon incision 8–10 mm posterior to the limbus. D, Anterior dissection of conjunctiva–Tenon flap with excision of Tenon episcleral fibrous adhesions.
(Parts A, C, and D modified with permission from Weinreb RN, Mills RP, eds. Glaucoma Surgery: Principles and Techniques. 2nd ed. Ophthalmology Monograph 4. American Academy of Ophthalmology; 1998:29–31. Part B courtesy of Robert D. Fechtner, MD.)
Fornix-based trabeculectomy with running closure.
Courtesy of James A. Savage, MD.
A partial-thickness scleral flap is created in the superior sclera, posterior to the limbus (Fig 7-13). This flap will ultimately cover the hole that allows aqueous to egress into the subconjunctival space. Whenever possible, the scleral flap is centered at 12 o’clock to help prevent postoperative bleb exposure and dysesthesia. Common flap shapes include triangular, rectangular, and trapezoidal.
Figure 13-7 Clinical photographs showing creation of a scleral flap 4 mm wide and 2.0–2.5 mm from front to back at 50%–75% scleral depth. A, Posterior margin is dissected with a fine blade. B, Crescent knife is used to dissect a partial-thickness scleral tunnel. C, Sides of the tunnel are opened to create a flap. D, Final appearance.
(Courtesy of Keith Barton, MD. Reproduced with permission of Moorfields Eye Hospital.)
A paracentesis provides access to the anterior chamber to allow re-formation of the chamber with balanced salt solution or viscoelastic when needed. An incision into the anterior chamber is created under the scleral flap with a sharp blade. A corneoscleral block of tissue is removed (Fig 8-13), creating a fistula that allows aqueous to flow directly from the anterior chamber to the subconjunctival space. The fistula can be made freehand or with a trephining device such as a Kelly Descemet membrane punch. This fistula is typically centered underneath the scleral flap and is small enough so that the flap overlaps it on all sides.
An iridectomy prevents iris from occluding the fistula (Fig 13-8D). Some surgeons do not perform an iridectomy in selected patients, as it is believed the risk of fistula occlusion is low in certain pseudophakic eyes. The risks of iridectomy (bleeding, inflammation) should be weighed against the risk of fistula obstruction.
Figure 13-8 The surgeon can create a fistula by (A) inserting a punch under the scleral flap; (B) snaring the posterior lip of the anterior chamber entry site; and (C) removing a punch (0.75–1.0 mm) of peripheral posterior cornea. A peripheral iridectomy (D) is then made (shown here in an albino eye) with iridectomy scissors.
(Clinical photographs courtesy of Keith Barton, MD; illustration based on original drawing by Alan Lacey. All parts reproduced with permission of Moorfields Eye Hospital.)
Closure of scleral flap and conjunctiva
The scleral flap is secured (Fig 9-13) with several nylon sutures (typically 10-0 or 9-0), which are tightened to provide appropriate resistance to aqueous flow. Some surgeons preplace these sutures before entering the anterior chamber to facilitate quick closure. Releasable sutures in the flap allow for suture removal postoperatively without a laser (Video 13-3). After the sutures are tied, the anterior chamber is re-formed with balanced salt solution, and scleral flap tension is titrated to achieve the desired rate of egress of aqueous humor.
Placement of a releasable suture for flap closure.
Courtesy of Marlene Moster, MD.
Conjunctival closure must be watertight to prevent postoperative complications and to maximize the success of the surgery. For a limbus-based flap, the Tenon capsule and conjunctiva are closed separately or in a single layer by means of a running suture on a vascular needle. For a fornix-based trabeculectomy, the conjunctiva can be closed with 2 wing sutures or a running suture.
Figure 13-9 In a trabeculectomy with mitomycin C, the scleral flap is closed relatively tightly so that spontaneous drainage is minimal. Closure may be performed with releasable sutures (A, B) that can be removed later at the slit lamp in order to increase flow or with interrupted sutures that can be cut postoperatively by laser. Part B shows the sequence of movements for placing 1 type of releasable suture. The surgeon should check the flow at the end of scleral closure using a sponge (C) or fluorescein (D).
(Clinical photographs courtesy of Keith Barton, MD; drawing courtesy of Alan Lacey. All parts reproduced with permission of Moorfields Eye Hospital.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.